Several components (crank journals etc.,) of internal combustion engines are supplied with oil by an oil circulation system while the internal combustion engine is operating. The oil circulation system makes oil circulate between an oil pan storing oil and parts supplied with oil.
PLT 1 describes that the temperature of the oil supplied to the parts supplied with oil is increased by utilizing the heat of the exhaust gas, in order to lower the mechanical resistance of the parts supplied with oil to improve the fuel efficiency of an internal combustion engine. Specifically, while the internal combustion engine is warming up, a part of the oil is run through oil paths near the exhaust ports so as to heat the oil by the high temperature exhaust gas in the exhaust ports.